Ex refuses to pay loan as agreed

My wife and I were separated over a year ago, and agreed on no alimony or child support, just simple joint custody in which we’d alternate weeks keeping the kids. In our separation agreement, my ex-wife agreed to pay half of what was then a $1000 a month loan payment. The loan was a large bill consolidation that was done during our marriage and was co-signed by my parents. 6 months later, the loan was up for renewal, and my ex refused to sign the loan renewal or pay her half of the monthly bill. The payment was reduced to $850 a month, which I have been paying all of by myself for the last 6 months. As a result of this change, we agreed that our 2 kids would stay with her during the week, and I would only keep them Friday through Sunday every other weekend, just to help offset some of the extra expense to me.

Our divorce is final now - a simple divorce with no alimony, child support or anything. She now wants me to keep the kids more, which I would really love to do, but frankly the extra $350 a month I’m paying really sticks in my craw. Do I have any legal recourse here? Can I legally hold her to paying half of the loan that she agreed to?

Unless you have a Separation Agreement outlining her obligation to pay towards the loan you do not have recourse on that front. You can however seek child support even now that the divorce is final.

The separation agreement stipulates that we are to each pay half of the loan. The loan had to be renewed last May because it was a 1 year loan with a balloon payment at the end (with the intention of renewing it yearly). She refused to sign the loan renewal (which is now termed out over 4 years), so it is now in my name only but still cosigned by my parents. Is she still legally responsible for half of the loan?

Yes, pursuant to the Agreement she is, and you may sue for breach of contract for her failure to abide by the terms.